Definition: In the present disclosure, the term “tactile display” is intended to refer to a display having a plurality of pins moving through a reference plane so as to be relatively raised or non-raised with respect thereto, and whose relative position of extension may be sensed by touch, typically by a person's fingers, although optionally by other body portions. In the present context, the “reference plane” may be flat or curved, and may be ‘real’, namely, defined by the surface of a physical element, or virtual.
The visually impaired typically require specialized interfaces for interacting with a computer as well as with other electronic devices, such as cellular phones. Tactile display devices are used to provide a tactile output for displaying information to computer users who are visually impaired, for example, by converting text to a format, such as Braille, that can be felt by the user.
Representative of the prior art, is U.S. Pat. No. 7,436,388 to Hillis et al, in which there is described a tactile display employing a plurality of pins for selectable movement so as to deform a flexible display surface thereon. Referring to FIG. 2, Hillis teaches a rectangular pin array arranged in rows and columns. As opposed to more traditional Braille displays in which a single actuator is provided for each pin, Hillis provides a system in which the number of actuators is equal to number of rows plus number of columns plus one. All of the pins 101 have relatively narrow stem portions 102 which protrude through a stationary plate 103. Each pin 101 employs a compression spring 104 which is adapted to urge it into a normally closed or down position, with respect to plate 103. A single movable pushing plate 107 is employed to raise the entire plurality of pins 101 in the array by applying a force H, against the urging S of the springs 104, and against a force R applied by the user and the self weight of the flexible display surface 108 which overlays the free end of the pin. Each pin 101 further includes a leveler or protrusion 105 which cooperates with a stopper 106 so as to prevent a downward movement of the pin 101 beyond a predetermined position.
Disadvantages of such configuration include the following:                1. In order to move a plurality of k pins from their lowest, retracted positions to their starting/extended positions, an actuator of the pushing plate 107 must work against external forces R which are applied to the top end of the pins 102 and the compressive resistance of the springs i.e. H>k*(R+S). Therefore, in practice, so as not to inadvertently prevent the extension of selected pins during a refreshing of the display, the user has to remove his fingers from the display at that time.        2. The leveler 105 of each pin 101 and each associated stopper 106, work not only against the compressive force of spring 104, but also against external forces, as described. As the overall construction of this prior art display is relatively delicate, and when this external force exceeds a certain limit, this can lead to the mechanical failure of the pin, as well as distortion of the leveler and/or stopper.        3. For multi-level displays, if R+S is too big, the pin may be pushed beyond a required location so as to inadvertently change the information sought to be displayed.        
Among other disadvantages of prior art generally, are high costs due to the large number of actuators required, the large amount of energy required for operation, long display refresh time.